The application of TEM to the study of helium cluster nucleation and growth in molybdenum at 300 K

Abstract

The addition of transmission electron microscopy (TEM) to monitor helium cluster nucleation and growth in molybdenum at ambient temperatures, has provided a useful extension to the information obtained in detailed helium desorption spectroscopy (HDS) studies. In particular, advantage has been taken of HDS helium filling techniques which allow the production of well characterized specimens containing a known number of helium atoms at a controlled low density of helium trapping centres. The problems of very dense damage structures found after conventional helium implantations have thus been avoided. This paper summarizes the filling techniques relevant to the production of TEM specimens together with the main results to date, e.g. the platelet morphology of helium cavities, their growth by loop punching, their transformation to groups of small bubbles, electron beam induced loop punching, and helium trapping at dislocations. The application of these results to the defect structures found in conventional implants is discussed.